Organizations may ask to use your facilities. Being a good neighbor suggests you should be open to helping people. Being a good steward suggests you take steps to avoid paying a claim arising from an activity your church didn't sponsor. This whitepaper discusses such topics as:

Planning for Big Success with Small Groups
Going Outside the Church Walls
Lending Your Church Facilities: Guidelines
Breaking Down the Age Barriers: How Churches Become Intentionally Intergenerational
Making Multisite Mergers Work: New Options for Being One Church in Two or More Locations